We propose to continue our combined in vitro/in vivo studies of lung growth and maturation. Lung growth: Based on previous observations that post-pneumonectomy lung hyperplasia in the rabbit is associated with a serum somatomedinlike substance, we propose to continue pursuing such observations in the rat. In this species, serum somatomedin C (SMC) falls post-pneumonectomy, nephrectomy, or sham surgery. However, the time course of return towards baseline is much more rapid in the two groups with hypertrophying organs. We propose that his represents a paracrine, rather than endocrine, phenomenon and will prepare short term explant cultures from regenerating (and control) organs and determine their generation of SMC in vitro. Lung development: We shall continue our studies of fibroblast-pneumonocyte factor (FPF) production and effects. Partially purified FPF from BioGel P60 chromatography has been fractionated by SDS-PAGE electrophoresis. BALB-C mice are being immunized with the 5 bands resolved. If blocking activity against FPF bioactivity in vitro is generated, spleen cells will be raised to prepare hybridomas in an attempt to develop monoclonal antibodies. Studies of thyroid hormone effects on FPF production and action are being continued.